In the current Hematology Analyzer, the control of flow passage is relatively complex due to a number of tubes, large flow of fluid and high requirement for clearness. In addition, since the fluid in the flow passage has strong corrosiveness, leakage of the fluid is not permitted. In order to meet these requirements, a solenoid valve and a solenoid pinch valve are generally used to intercept and release the fluid in the flow passage.
For the solenoid valve, the fluid directly contacts with a valve cavity and a valve port of the solenoid valve during passing though the solenoid valve. Due to the construction of the solenoid valve, it is hard to prevent the residual contamination resulted from the dead region inside the solenoid valve which can not be cleaned during cleaning the solenoid valve. Moreover, the pressure loss is relatively large when the fluid flows through the solenoid valve. Therefore, such a solenoid valve is only adapted to such a case that the clearness is not required, corrosiveness of fluid is not strong and the fluid flow is not large.
For the solenoid pinch valve, as shown in FIGS. 1 and 2, a distance between a pressing piece 4 and a lever 5 is adjusted by controlling the movement of the pressing piece 4, so as to selectively pinch or release a relatively soft fluid tube 1 therebetween. When the fluid tube 1 is pinched and thus the opposite inner walls of the fluid tube 1 contact with each other in a closed state (i.e in a contacting-closed state), the fluid in the fluid tube 1 is intercepted; when the fluid tube 1 is released, the fluid is allowed to flow through the fluid tube 1. As a result, the interception and the release of the fluid in the fluid tube 1 are achieved. The above control is characterized in that the interception and release of the fluid is realized along a tube, and the fluid does not directly contact the solenoid pinch valve which only provides a pinching force from the outside of the fluid tube. Therefore, the residual contaminant, corrosion and leakage in the solenoid pinch valve will be completely avoided, the pressure loss does not exist, and the flow of fluid through the fluid tube is not affected at all. However, the above control has the following defects: heavy defect will be presented in the case of long-time interception and short-time release. If the normal-opening type of solenoid pinch valve is used, the solenoid pinch valve will operate with electricity for long time during the interception of the fluid, so that the amount of the generated heat is large and the durability of the solenoid pinch valve will be affected. If a normal-closing type of solenoid pinch valve is used, there is no problem during operation of the solenoid pinch valve, but when the solenoid pinch valve is not in the operating state, the fluid tube is always in the pinched state, which might result in fatigue break of the fluid tube and the adhesion of the inner wall thereof the fluid tube and. For assuring enough pinching force, the solenoid pinch valve is relatively bulky; however, since the heat productivity of bulky solenoid pinch valve is relatively high, the heat dissipation should be considered in the case that the valve operates for a long time and in the case that multiple solenoid pinch valves operate at the same time. In addition, the optimal pressed state can not be set according to different materials and different wall thicknesses of the fluid tubes. Noise is large during operation of the solenoid pinch valve and the manufacturing cost of the solenoid pinch valve is high.